Using a Drosophila tumor model in a genetic screen, we previously completed a genome-wide screen for mutations that cooperate with oncogenic Ras in promoting tumor growth and metastasis. Characterization of several identified mutations revealed unexpected biology and pathways, and especially highlighted the importance of cell-cell interaction and signaling in mediating tumor development and progression. Disruption of cell junction or apical-basal polarity leads to JNK activation, which is essential for tumor cell survivl, basement membrane degradation, tumor cell migration, and the unexpected behavior of interclonal cooperation with oncogenic Ras in promoting tumor growth and metastasis. Indeed, the behavior of tumor cells has long been recognized to be highly influenced by its microenvironment, interaction with surrounding wild type cells, and the extracellular milieu such as components of the extracellular matrix. The focus of our research, thus, logically switches from identifying the involved genes in the current funding period to uncover the molecular, cellular, and developmental mechanisms underlying tumor and host cell interactions for tumor growth and metastasis. We propose the following specific aims: (1) Characterizing novel RasV12 cooperating mutations and mechanisms related to JNK activation. We will characterize several new mutations/genes identified in our screen with the aim to identify and study novel tumor suppressors and to understand how JNK is activated. Our efforts will be focused on characterizing novel RasV12 cooperating mutations/genes that have mammalian orthologs mutated in human cancers and those genes that could help us to understand the causal link between disruption of cell polarity and JNK signaling in tumor development; (2) Dissecting cell-cell interaction and signaling mechanisms in promoting tumor growth and metastasis. We will further dissect the signaling between tumor and surrounding wild type cells that promotes tumor development, and will also characterize a novel tumor suppressor, which defines a new mode of cell-cell interaction via unique multicellular epithelial contacts; and (3) Studying organ-specific metastasis. We have discovered that the fly tumors also exhibit organ-specific metastasis behavior, and will try to identify the molecular basis for this targeted migration and invasion. In summary, having identified causative mutations for epithelial tumors, we are now poised to utilize the power of the Drosophila model organism to explore and unravel the molecular mechanisms underlying intercellular signaling that is central to the understanding of cancer biology.